Various organs of the gastrointestinal tract such as the stomach, small intestine and colon contain cells that are believed to govern the organs' periodic contractile behavior. In healthy humans, in certain regions of the organs, these cells generate and propagate rhythmic electrical signals. In general, several types of electrical potential activity have been observed in the gastrointestinal tract. Consistent cyclic slow wave or pacesetter potentials have been observed and higher frequency spike activity has been observed that may correspond to some extent with smooth muscle contractile activity and peristalsis. The stomach and digestive system is also controlled by the nervous system that includes a highly complex enteric nervous system and to some extent, the central nervous system. It is believed that when the pacesetter potentials are combined with a chemical or neural excitation of the cells that smooth muscle contractile activity occurs. It is also believed that stimulation of the stomach may effect a subject's sensation of satiety through a complex system involving smooth muscle stimulation or contractions, and neural and chemical pathways.
Obesity has become one of the leading causes of death in the United States. Electrical stimulation has been proposed to treat obesity by causing a feeling of satiety, for example, by altering gastric motility. Some electrical stimulation is believed to interfere with the electrical potential activity of the stomach and to slow the movement of food through the stomach. Electrical stimulation may cause the stomach to retain food for a greater duration. This gastric retention among other factors may induce a sensation of satiety.
Electrical stimulation of the gastrointestinal tract has also been proposed to treat motility related disorders and other gastrointestinal diseases. The electrical stimulation has been proposed in a number of forms or for a number of applications, such as, e.g., pacing, electrical contractile stimulation or other stimulation.
In some disease states, dysrhythmias of the gastric pacesetter potentials may be present. Electrical pacing of gastric pacesetter potentials has been proposed to induce regular rhythms for the pacesetter potentials with the intent of inducing regular or controlled gastric contractions. The result of abnormal pacesetter potentials may be gastric retention of food. Electrical stimulation of gastric tissue has also been proposed to induce peristalsis. Electrical stimulation has also been proposed to slow the gastric emptying to treat a disorder known as dumping syndrome where the stomach empties at an abnormally high rate into the small intestine causing various gastrointestinal disorders.
An early attempt at a gastric stimulation device included an electrode at the end of a nasogastric tube or catheter. The nasogastric tube was passed into the stomach transnasally. Electrical stimulation was applied using an external stimulator unit through the electrode on the end of the tube. The return electrode was placed on the abdomen. This device required a transnasal procedure whenever stimulation was required.
Other devices used to pace the stomach have generally been implanted by accessing the outside of the stomach through an opening in the abdomen, either through open surgery or laparoscopic surgery. Electrodes have been attached to the stomach laparoscopically with attached leads extending through the abdomen to a subcutaneously or sub-muscularly implanted electronics unit. The devices may be anchored into the subcutaneous or sub-muscular pocket initially by a suture anchor and/or eventually by fibrous tissue ingrowth around the unit.
Other devices are described, for example in related U.S. Pat. No. 6,535,764, fully incorporated herein by reference. U.S. Pat. No. 6,535,764 describes a gastric stimulator that is implanted by delivering the device through the esophagus of a subject and attaching to the stomach wall from the inside of the stomach. Also, related U.S. patent application Ser. No. 10/109,296, fully incorporated herein by reference, describes a gastric stimulator that is implanted submucosally within the stomach wall.
Some gastric stimulation procedures have proposed electrical stimulation in response to sensing innate electrical pulses within the stomach that fall within particular ranges. According to these procedures, sensing electrical signals are indicators of when or how to stimulate or when or how to stop stimulation. Additionally, a device has been proposed to sense electrical parameters to determine the fullness of an organ and the absence of muscular contraction, and to deliver electrical muscular contraction stimulation to the organ in response (i.e., presumably to treat gastro-paresis). However, some sensed electrical signals are not reliably detected and have not always corresponded with appropriate indicators of need for stimulation.
A gastrointestinal stimulator has be described that senses food being swallowed by sensing motion (with an accelerometer), temperature, or pressure and responsively stimulates to coordinate contractions in various gastrointestinal organs to prevent esophageal acid reflux or, to increase speed of movement of food through the gastrointestinal tract (under the theory that less food will be absorbed when food moves more quickly through the stomach). As described, the stimulator stimulates when the gastrointestinal tract fails to act normally. While there has been some success in gastric stimulation, it is believed that over time the stomach may become desensitized to ongoing stimulation. Therefore, it would be desirable to provide a gastric stimulator that reduces desensitization of the stomach from ongoing stimulation.
Also, implanted stimulators have limited battery life, particularly when the device is smaller. Accordingly, it would be desirable to provide a device that operates to conserve battery life.
It would be desirable to provide a gastric stimulator that stimulates the stomach under predetermined circumstances or conditions or at appropriate times.
It would further be desirable to provide such a stimulator that stimulates in order to produce a sensation of satiety.
Furthermore, to control eating disorders or to treat obesity, it would be desirable to provide a stimulator that senses when food has been ingested and/or can regulate stomach contractions based on identification of the contents of the stomach or according to an eating regimen.